why are these mentioned twice?
could it be that the "rock" is Peter AND his faith is that too? in different ways? why would Pope Leo and Augustine seem to teach both otherwise?
this is a sincere question.
What is most interesting here is that even the Catechism of the Catholic Church speaks of Jesus as the Rock, the Apostles as the Rock, and St. Peter as the Rock.
Biblical passages usually have only one literal meaning, but can have several applications and interpretations. So whereas the passage of Matt. 16 is literally and primarily to be understood as a reference to a comission to St. Peter (which is the most numerously applied meaning of this passage by the Fathers of the Church), the passage can also be marshaled in defense of Jesus' Divinity or of the need for Divine Revelation. When the Father use this passage to refer to the Rock as Christ, or Peter's confession, or faith, they are
not denying the literal meaning of the passage a meaning that they themselves testify to with great force. The Fathers are simply (like the Catechism of the Catholic Church) utilizing the richness of Holy Scripture for apologetic resources.
St. Peter's commission in Matt. 16 can be understood and used in various ways, HOWEVER these useful applications do NOT negate the primary and literal interpretation, which again is so powerfully attested to by the Fathers.
It is all too wrong (and not in keeping with the Fathers) to make these less literal interpretations of the passage to be proofs of an "either-or" dichotomy. The position of the Fathers, made quite clear by them, is a "both-and" position and is held by the Catholic Church even today.
The Catechism of the Catholic Church says:
"On the rock of this faith confessed by St. Peter, Christ built His Church."
Mixing the metaphors does damage to the text and the intent of the Biblical passages. In Matt. 16 we find St. Peter as the foundation, Christ the builder, and the believers the building stone. In 1 Cor. 3 however, Christ is the foundation (not said to be the builder), the apostles are the builders, and the building material is good or worthless work. The Matthean passage deal with the Church as a whole, whereas the second deals with the individual Christian. We must not mix the metaphors and create needless dichotomies as this "divides the word of truth."
Here: lets take a look at St. Hilary of Pontiers.
St. Hilary said that the faith of St. Peter is that which held the keys to the kingdom. However in a few chapters back in that same work (On the Trinity 6,37,121) St. Hilary says that St. Peter himself is the foundation stone of the Church. Are we then to assume that St. Hilary is confused!
No, we must ask ourselves whether St. Hilary sees these two affirmations as "mutually exclusive" or whether he sees no conflict between the two in accord with what I discussed above.
Even Pope John Paul the Great (of blessed memory) said in his "Crossing the Threshold of Hope" that:
"He [Peter] became the 'rock,' even if as a man, perhaps, he was nothing more than shifting sand. Christ Himself is the Rock
and Christ builds His Church on Peter...on Peter, Paul, and the Apostles. The Church is Apostolic
in virtue of Christ.....In the Church built on the Rock that is Christ, Peter, and the Apostles are witness of God crucified and risen in Christ."
Again let me quote the modern Catholic Catechism:
552 Simon Peter holds the first place in the college of the Twelve; Jesus entrusted a unique mission to him. Through a revelation from the Father, Peter had confessed: "You are the Christ, the Son of the living God." Our Lord then declared to him: "You are Peter, and on this rock I will build my Church, and the gates of Hades will not prevail against it." Christ, the "living Stone", thus assures his Church, built on Peter, of victory over the powers of death. Because of the faith he confessed Peter will remain the unshakable rock of the Church. His mission will be to keep this faith from every lapse and to strengthen his brothers in it.
Yet the Catechism also says:
424 Moved by the grace of the Holy Spirit and drawn by the Father, we believe in Jesus and confess: 'You are the Christ, the Son of the living God. On the rock of this faith confessed by St. Peter, Christ built his Church.
Like the Fathers, the Catholic Church continues to view this in the Patristic manner. The Fathers used Matthew 16 in many ways, as does the Catholic Church today.
None of it necessitates the creation of artificial dichotomies in order to prove a point that, ultimately, is contrary to the profession of the Fathers, who never seemed to talk about other ways of Matt. 16 without also speaking of the literal perspective held by the Catholic Church, East and West, even today.